From: Boris Brezillon <boris.brezillon@collabora.com> To: Sean Nyekjaer <sean@geanix.com> Cc: Miquel Raynal <miquel.raynal@bootlin.com>, Richard Weinberger <richard@nod.at>, Vignesh Raghavendra <vigneshr@ti.com>, Boris Brezillon <bbrezillon@kernel.org>, linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mtd: rawnand: use mutex to protect access while in suspend Date: Mon, 4 Oct 2021 10:41:47 +0200 [thread overview] Message-ID: <20211004104147.579f3b01@collabora.com> (raw) In-Reply-To: <20211004065608.3190348-1-sean@geanix.com> On Mon, 4 Oct 2021 08:56:09 +0200 Sean Nyekjaer <sean@geanix.com> wrote: > This will prevent nand_get_device() from returning -EBUSY. > It will force mtd_write()/mtd_read() to wait for the nand_resume() to unlock > access to the mtd device. > > Then we avoid -EBUSY is returned to ubifsi via mtd_write()/mtd_read(), > that will in turn hard error on every error returened. > We have seen during ubifs tries to call mtd_write before the mtd device > is resumed. I think the problem is here. Why would UBIFS/UBI try to write something to a device that's not resumed yet (or has been suspended already, if you hit this in the suspend path). > > Exec_op[0] speed things up, so we see this race when the device is > resuming. But it's actually "mtd: rawnand: Simplify the locking" that > allows it to return -EBUSY, before that commit it would have waited for > the mtd device to resume. Uh, wait. If nand_resume() was called before any writes/reads this wouldn't happen. IMHO, the problem is not that we return -EBUSY without blocking, the problem is that someone issues a write/read before calling mtd_resume(). > > Tested on a iMX6ULL. > > [0]: > ef347c0cfd61 ("mtd: rawnand: gpmi: Implement exec_op") > > Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking") > Signed-off-by: Sean Nyekjaer <sean@geanix.com> > --- > > I did this a RFC as we probably will need to remove the suspended > variable as it's kinda made obsolute by this change. > Should we introduce a new mutex? Or maybe a spin_lock? > > drivers/mtd/nand/raw/nand_base.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > index 3d6c6e880520..0ea343404cac 100644 > --- a/drivers/mtd/nand/raw/nand_base.c > +++ b/drivers/mtd/nand/raw/nand_base.c > @@ -4567,7 +4567,6 @@ static int nand_suspend(struct mtd_info *mtd) > ret = chip->ops.suspend(chip); > if (!ret) > chip->suspended = 1; > - mutex_unlock(&chip->lock); Hm, I'm not sure keeping the lock when you're in a suspended state is a good idea. It just papers over another bug IMO (see above). > > return ret; > } > @@ -4580,7 +4579,6 @@ static void nand_resume(struct mtd_info *mtd) > { > struct nand_chip *chip = mtd_to_nand(mtd); > > - mutex_lock(&chip->lock); > if (chip->suspended) { > if (chip->ops.resume) > chip->ops.resume(chip);
WARNING: multiple messages have this Message-ID (diff)
From: Boris Brezillon <boris.brezillon@collabora.com> To: Sean Nyekjaer <sean@geanix.com> Cc: Miquel Raynal <miquel.raynal@bootlin.com>, Richard Weinberger <richard@nod.at>, Vignesh Raghavendra <vigneshr@ti.com>, Boris Brezillon <bbrezillon@kernel.org>, linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mtd: rawnand: use mutex to protect access while in suspend Date: Mon, 4 Oct 2021 10:41:47 +0200 [thread overview] Message-ID: <20211004104147.579f3b01@collabora.com> (raw) In-Reply-To: <20211004065608.3190348-1-sean@geanix.com> On Mon, 4 Oct 2021 08:56:09 +0200 Sean Nyekjaer <sean@geanix.com> wrote: > This will prevent nand_get_device() from returning -EBUSY. > It will force mtd_write()/mtd_read() to wait for the nand_resume() to unlock > access to the mtd device. > > Then we avoid -EBUSY is returned to ubifsi via mtd_write()/mtd_read(), > that will in turn hard error on every error returened. > We have seen during ubifs tries to call mtd_write before the mtd device > is resumed. I think the problem is here. Why would UBIFS/UBI try to write something to a device that's not resumed yet (or has been suspended already, if you hit this in the suspend path). > > Exec_op[0] speed things up, so we see this race when the device is > resuming. But it's actually "mtd: rawnand: Simplify the locking" that > allows it to return -EBUSY, before that commit it would have waited for > the mtd device to resume. Uh, wait. If nand_resume() was called before any writes/reads this wouldn't happen. IMHO, the problem is not that we return -EBUSY without blocking, the problem is that someone issues a write/read before calling mtd_resume(). > > Tested on a iMX6ULL. > > [0]: > ef347c0cfd61 ("mtd: rawnand: gpmi: Implement exec_op") > > Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking") > Signed-off-by: Sean Nyekjaer <sean@geanix.com> > --- > > I did this a RFC as we probably will need to remove the suspended > variable as it's kinda made obsolute by this change. > Should we introduce a new mutex? Or maybe a spin_lock? > > drivers/mtd/nand/raw/nand_base.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > index 3d6c6e880520..0ea343404cac 100644 > --- a/drivers/mtd/nand/raw/nand_base.c > +++ b/drivers/mtd/nand/raw/nand_base.c > @@ -4567,7 +4567,6 @@ static int nand_suspend(struct mtd_info *mtd) > ret = chip->ops.suspend(chip); > if (!ret) > chip->suspended = 1; > - mutex_unlock(&chip->lock); Hm, I'm not sure keeping the lock when you're in a suspended state is a good idea. It just papers over another bug IMO (see above). > > return ret; > } > @@ -4580,7 +4579,6 @@ static void nand_resume(struct mtd_info *mtd) > { > struct nand_chip *chip = mtd_to_nand(mtd); > > - mutex_lock(&chip->lock); > if (chip->suspended) { > if (chip->ops.resume) > chip->ops.resume(chip); ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2021-10-04 8:42 UTC|newest] Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-10-04 6:56 [RFC PATCH] mtd: rawnand: use mutex to protect access while in suspend Sean Nyekjaer 2021-10-04 6:56 ` Sean Nyekjaer 2021-10-04 8:41 ` Boris Brezillon [this message] 2021-10-04 8:41 ` Boris Brezillon 2021-10-04 8:55 ` Sean Nyekjaer 2021-10-04 8:55 ` Sean Nyekjaer 2021-10-04 9:58 ` Boris Brezillon 2021-10-04 9:58 ` Boris Brezillon 2021-10-04 10:12 ` Sean Nyekjaer 2021-10-04 10:12 ` Sean Nyekjaer 2021-10-04 11:47 ` Boris Brezillon 2021-10-04 11:47 ` Boris Brezillon 2021-10-05 7:09 ` Sean Nyekjaer 2021-10-05 7:09 ` Sean Nyekjaer 2021-10-05 8:23 ` Boris Brezillon 2021-10-05 8:23 ` Boris Brezillon 2021-10-05 8:49 ` Sean Nyekjaer 2021-10-05 8:49 ` Sean Nyekjaer 2021-10-05 8:58 ` Boris Brezillon 2021-10-05 8:58 ` Boris Brezillon 2021-10-07 11:43 ` Sean Nyekjaer 2021-10-07 11:43 ` Sean Nyekjaer 2021-10-07 12:18 ` Boris Brezillon 2021-10-07 12:18 ` Boris Brezillon 2021-10-07 12:39 ` Sean Nyekjaer 2021-10-07 12:39 ` Sean Nyekjaer 2021-10-07 13:14 ` Boris Brezillon 2021-10-07 13:14 ` Boris Brezillon 2021-10-08 10:04 ` Sean Nyekjaer 2021-10-08 10:04 ` Sean Nyekjaer 2021-10-08 11:20 ` Boris Brezillon 2021-10-08 11:20 ` Boris Brezillon 2021-10-08 11:54 ` Sean Nyekjaer 2021-10-08 11:54 ` Sean Nyekjaer 2021-10-08 12:15 ` Boris Brezillon 2021-10-08 12:15 ` Boris Brezillon 2021-10-08 14:38 ` [RFC PATCH 1/2] mtd: core: protect access to mtd devices " Sean Nyekjaer 2021-10-08 14:38 ` Sean Nyekjaer 2021-10-08 15:30 ` Boris Brezillon 2021-10-08 15:30 ` Boris Brezillon 2021-10-08 17:31 ` Sean Nyekjaer 2021-10-08 17:31 ` Sean Nyekjaer 2021-10-08 15:35 ` Miquel Raynal 2021-10-08 15:35 ` Miquel Raynal 2021-10-08 16:08 ` Boris Brezillon 2021-10-08 16:08 ` Boris Brezillon 2021-10-08 17:50 ` Sean Nyekjaer 2021-10-08 17:50 ` Sean Nyekjaer 2021-10-08 14:38 ` [RFC PATCH 2/2] mtd: rawnand: remove suspended check Sean Nyekjaer 2021-10-08 14:38 ` Sean Nyekjaer 2021-10-08 22:05 ` kernel test robot 2021-10-08 22:05 ` kernel test robot 2021-10-08 22:47 ` kernel test robot 2021-10-08 22:47 ` kernel test robot
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